1. Field of the Invention
The present invention generally relates to ink jet heads and ink jet printers, and more particularly to an ink jet head which uses a thin film piezoelectric element as a means of jetting ink, and to an ink jet printer which uses such an ink jet head.
Most inexpensive color printers are ink jet printers which use the ink jet head, because ink jet head does not generate noise and the ink jet printer can realize color printing at a low cost compared to electrophotography printers.
Recently, there are demands to realize a high resolution by the ink jet printer, and rapid developments are being made to minimize the drop diameter of the ink which is jetted from the ink jet head. Moreover, there are demands to realize an ink jet printer having a structure suited for mass production, while satisfying the demands to realize a high performance.
2. Description of the Related Art
FIG. 1 is a diagram showing an example of an ink jet printer. An ink jet printer 10 shown in FIG. 1 includes an ink jet head 11 which is mounted on a lower surface of a carriage 12. This ink jet head 11 is positioned between a feed roller 13 and an eject roller 14, and confronts a platen 15. The carriage 12 has an ink tank 16, and is movable in a direction perpendicular to a drawing paper on which FIG. 1 is drawn.
A paper 17 is pinched between a pinch roller 18 and the feed roller 13, and is transported in a direction A in a state pinched between a pinch roller 19 and the eject roller 14. The ink jet head 11 prints on the paper 17 when the ink jet head 11 operates and the carriage 12 moves in the direction perpendicular to the drawing paper. After the printing, the paper 17 is accommodated within a stacker 20.
FIG. 2 is a perspective view showing an important part of an ink jet head. As shown in FIG. 2, an ink jet head 30, which corresponds to the ink jet head 11 described above, includes a nozzle plate 33 formed with nozzles 32 from which ink is jetted, pressure chambers 35 and ink passages 40 which are respectively formed in correspondence with each of the nozzles 32, a driving part 31 forming one wall of each of the pressure chambers 35, a common ink passage 39 for supplying the ink to each of the pressure chambers 35, and a main body 36. The pressure chambers 35 and the common ink passage 39 are integrally formed in the main body 36.
The driving part 31 includes piezoelectric elements 37 which are provided with respect to each of the pressure chambers 35 on a vibration plate 34 which forms one wall of each of the pressure chambers 35 in common. The vibration plate 34 also forms the common electrode of each piezoelectric element 37. Individual electrodes 38 are provided on the top surface of the corresponding piezoelectric elements 37. The driving part 31 forms a bimorph structure by the piezoelectric elements 37 and the vibration plate 34. When a driving signal from a controller is applied on the individual electrode 38, the corresponding piezoelectric element 37 is distorted so as to contract in an in-plane direction of the vibration plate 34. Hence, the driving part 31 deforms towards the corresponding pressure chamber 35 as indicated by a phantom line in FIG. 2, and the ink drop is jetted from the corresponding nozzle 32. When the driving signal is no longer applied to the individual electrode 38, the driving part 31 is restored to the flat non-deformed state, thereby supplying the ink from the common ink passage 39 to the corresponding ink chamber 35.
According to such a bimorph structure, it is possible to obtain a large volume displacement with respect to a small distortion of the piezoelectric element without requiring complex structure for fixing piezoelectric element end. For this reason, this bimorph structure is suited for mass production.
When forming the bimorph structure, a plate-shaped piezoelectric element base is cut into a plurality of narrow piezoelectric elements, and the piezoelectric elements are fixed on the vibration plate by means of an adhesive agent or the like. But because of this structure, the piezoelectric element may come off from the vibration plate when the piezoelectric element is greatly deformed, and there is a problem in that it is difficult to form an ink jet head having a satisfactory printing efficiency. Furthermore, since it is necessary to carry out a process of fixing the mechanically cut piezoelectric elements on the vibration plate, it is difficult to miniaturize the pressure chambers and the piezoelectric elements.
On the other hand, a relatively small bimorph structure can be made by forming the piezoelectric elements by use of the printing technique. In other words, a common electrode is formed on a vibration plate which is made of a highly heat resistant material such as ceramics, and a paste of the material which forms the piezoelectric elements is formed and patterned on the vibration plate by use of the screen printing technique, and then baked. It is difficult to increase the density of the piezoelectric elements having this structure because the piezoelectric elements are formed by use of the printing technique, and in addition, the piezoelectric elements formed are brittle mechanically and electrically. As a result, there is a problem in that the piezoelectric element breaks when the piezoelectric element is greatly deformed. Consequently, it is necessary to increase the area of the pressure chambers and the piezoelectric elements as much as possible, in order to compensate for the small tolerable deformation of the piezoelectric elements.
However, according to the method which forms the bimorph structure using the printing technique, it is difficult to mass produce the piezoelectric elements having a thickness of less than 15 xcexcm. For this reason, the pressure chamber must have a width of at least 200 xcexcm in order to mass produce the ink jet heads having a satisfactory printing efficiency, and the pitch of the nozzles cannot be made small.
On the other hand, in order to make the piezoelectric element thin, it is possible to use the thin film technique such as sputtering, instead of using the screen printing technique. But when the thin film technique is used, the thickness of the piezoelectric element on the order of several tens of xcexcm is too thick for mass production, in that it takes too much time to form such a thick layer by the thin film technique. Hence, if an attempt is made to use a piezoelectric element having a thickness on the order of only several xcexcm which can be formed by the thin film technique, it is impossible to generate a sufficiently large pressure with respect to the ink due to the bimorph structure if the size of the pressure chamber is the same as that for the thick piezoelectric element having the thickness of less than 15 xcexcm. As a result, it is impossible to obtain a sufficiently large volume displacement by use of such a thin piezoelectric element.
Furthermore, if the size of the pressure chamber with respect to the thin piezoelectric element is reduced to the same proportion as the size of the pressure chamber with respect to the thick piezoelectric element, the pressure chamber becomes too small. Consequently, the ink drop which can be jetted by the combination of the thin piezoelectric element and the small pressure chamber becomes extremely small, that is, only on the order of a fraction of 1 pl or less, where 1 pl=10xe2x88x9212 1=10xe2x88x9215 m3.
It is possible to arrange the nozzles at a small pitch when the pressure chamber is small, and a high-quality image can be printed when the ink drop is small, thereby making it possible to realize a high-performance ink jet head. However, the ink drop must be at least 2 pl in order for a corresponding printed dot to be recognizable by the human eyes, and for this reason, the image quality cannot be improved even if the printing is carried out using ink drops smaller than 2 pl.
In addition, various problems are introduced when an attempt is made to print by use of the combination of the thin piezoelectric element and the small pressure chamber which jets ink drops on the order of a fraction of 1 pl, for example. First, the nozzles must be made small in order to produce the small ink drops, but such small nozzles easily clog. When nozzles are clogged, it is essential to remove the clog by use of a backup unit. Second, when the ink drop is small, the ink drop jetted from the nozzle is greatly affected by air friction before reaching the paper surface, and the accuracy of the landing position of the ink drop deteriorates. Third, in order to obtain a required printing density, the amount of dye or coloring material required per unit area is approximately the same regardless of the size of the ink drop, and for this reason, it takes an extremely long time to carry out the printing because an extremely large number of dots must be printed by the small ink drops in order to obtain a printing density which is comparable to the conventional printing density.
Therefore, the ink jet head using the piezoelectric elements produced by the thin film technique is unsuited for realizing a high reliability. Hence, such an ink jet head is unsuited for use in a general purpose printer.
In addition, in order to eliminate the problem of the extremely long printing time, it is possible to eliminate this problem by increasing the number of nozzles. However, as the number of nozzles becomes large, the number of signal lines, the number of driver circuits which drive the piezoelectric elements, and the number of signal line connections all become large, thereby requiring a large number of production processes. Furthermore, the use of a high-performance processor becomes necessary in order to process a large amount of data, and the printer becomes too expensive from the practical point of view. Moreover, when the amount of data to be processed becomes large, a large amount of data is sent from a computer, thereby requiring a high-speed channel for transferring the printing data. As a result, it may become impossible to cope with the large amount of data and the required speed using a standard interface.
Accordingly, it is a general object of the present invention to provide a novel and useful ink jet head and ink jet printer, in which the problems described above are eliminated.
Another and more specific object of the present invention is to provide an ink jet head comprising a pressure chamber, a vibration plate, and a piezoelectric element, provided on the vibration plate, causing a volume displacement of the pressure chamber, where the piezoelectric element has a thickness of 20 xcexcm or less, and the pressure chamber and the piezoelectric element satisfy a relation V0/(L22b) greater than 550xc3x9710xe2x88x926, where V0 [m3] denotes a volume displacement of the pressure chamber when the piezoelectric element is driven, L2 [m] denotes a width of the piezoelectric element, and b [m] denotes a depth of the pressure chamber. According to the ink jet head of the present invention, it is possible to produce ink jet heads having a high printing performance with a high productivity.
Still another object of the present invention is to provide an ink jet head comprising a pressure chamber, a vibration plate, and a piezoelectric element, provided on the vibration plate, causing a volume displacement of the pressure chamber, where the piezoelectric element has a thickness of 20 xcexcm or less, the pressure chamber and the piezoelectric element satisfy a relation EV0/(L22b) greater than 30xc3x97106, where E [Pa] denotes a Young""s modulus of the piezoelectric element, V0 [m3] denotes a volume displacement of the pressure chamber when the piezoelectric element is driven, L2 [m] denotes a width of the piezoelectric element, and b [m] denotes a depth of the pressure chamber. According to the ink jet head of the present invention, it is possible to produce ink jet heads having a high printing performance with a high productivity, particularly when the piezoelectric element is formed by the thin film technique and the Young""s modulus E is large.
A further object of the present invention is to provide an ink jet head comprising a pressure chamber, a vibration plate, and a piezoelectric element, provided on the vibration plate, causing a volume displacement of the pressure chamber, where the piezoelectric element has a thickness of 20 xcexcm or less, the pressure chamber and a voltage applied to the piezoelectric element satisfy a relation V/h2 greater than 3.0xc3x97106, where V [V] denotes the voltage applied to the piezoelectric element, and h2 [m] denotes a thickness of the piezoelectric element. According to the ink jet head of the present invention, it is possible to produce ink jet heads having a high printing performance with a high productivity.
Another object of the present invention is to provide a multi-nozzle ink jet head comprising a pressure chamber connecting to a nozzle, a vibration plate which forms an upper wall surface of the pressure chamber, and a thin film piezoelectric element, provided on the vibration plate, causing a volume displacement of the pressure chamber, where the thin film piezoelectric element generates a piezoelectric effect in an in-plane direction of one surface of the vibration plate, the thin film piezoelectric element and the vibration plate have a total thickness of 10 xcexcm or less, and the nozzle has an ink jet quantity of 1 pl or greater when the piezoelectric element is driven, and is arranged at a pitch of 150 dots/inch or greater. According to the multi-nozzle ink jet head of the present invention, it is possible to mass produce ink jet heads having a high printing efficiency.
Still another object of the present invention is to provide an ink jet printer comprising an ink jet head including a pressure chamber, a vibration plate, and a piezoelectric element which is provided on the vibration plate and causes a volume displacement of the pressure chamber, wherein the piezoelectric element has a thickness of 20 xcexcm or less, the pressure chamber and the piezoelectric element satisfy a relation V0/(L22b) greater than 550xc3x9710xe2x88x926, where V0 [m3] denotes a volume displacement of the pressure chamber when the piezoelectric element is driven, L2 [m] denotes a width of the piezoelectric element, and b [m] denotes a depth of the pressure chamber. According to the ink jet printer of the present invention, it is possible to produce ink jet printers having a high printing performance with a high productivity.
A further object of the present invention is to provide an ink jet printer comprising an ink jet head including a pressure chamber, a vibration plate, and a piezoelectric element which is provided on the vibration plate and causes a volume displacement of the pressure chamber, wherein the piezoelectric element has a thickness of 20 xcexcm or less, the pressure chamber and the piezoelectric element satisfy a relation EV0/(L22b) greater than 30xc3x97106, where E [Pa] denotes a Young""s modulus of the piezoelectric element, V0 [m3] denotes a volume displacement of the pressure chamber when the piezoelectric element is driven, L2 [m] denotes a width of the piezoelectric element, and b [m] denotes a depth of the pressure chamber. According to the ink jet printer of the present invention, it is possible to produce ink jet printers having a high printing performance with a high productivity, particularly when the piezoelectric element is formed by the thin film technique and the Young""s modulus E is large.
Another object of the present invention is to provide an ink jet printer comprising an ink jet head including a pressure chamber, a vibration plate, and a piezoelectric element which is provided on the vibration plate and causes a volume displacement of the pressure chamber, wherein the piezoelectric element has a thickness of 20 xcexcm or less, the pressure chamber and a voltage applied to the piezoelectric element satisfy a relation V/h2 greater than 3.0xc3x97106, where V [V] denotes the voltage applied to the piezoelectric element, and h2 [m] denotes a thickness of the piezoelectric element. According to the ink jet printer of the present invention, it is possible to produce ink jet printers having a high printing performance with a high productivity.
Other objects and further features of the present invention will be apparent from the following detailed description when read in conjunction with the accompanying drawings.